While industrial process belts generally come in a wide variety of styles, they can generally be characterized as formed from a pattern of warp and shute yarns, which extend in the machine and cross machine direction. In another variant, belts are joined of spirally wound fibers or yarns, or in yet another variant, the belt may itself be produced from a spirally wound fabric strip. Some industrial belts can be single layer belts, or they may be multilayered. Some belts have one or more layers laminated together by processes such as needle punching, or held together by binder threads. Some belts, such as press fabrics, have nonwoven fiber attached by needling or hydroentangling. Any one of these belts may be coated or impregnated with a resin to impart certain characteristics to the belt or to modify existing characteristics. Belts used on papermaking machines are but one kind of industrial process belt. These belts are used in the forming, pressing, drying and finishing sections of a papermaking machine.
In the use of an industrial process belt, the operator of the machine would like to have information concerning the operating conditions of the belt and/or the product that is transported on the belt. For instance, it is important to place an accurate guide line upon the belt, since this guide line is used to determine the skew of the belt. While the belt runs on a machine, the cross machine direction filaments can skew, or in other words, bow. Skew is characterized by the bowing of the cross machine direction filaments. Skew can either be forward or backward with respect to the direction in which the belt runs. For instance, for a belt used to remove moisture from a paper product, the skew affects the permeability of the belt, with the permeability at the edges of the belt differing from the permeability in the center. Belt permeability is of great importance in the production of a wet laid product, such as a paper product, and hence the skew of the belt is of great interest to the machine operator. A change in the shape of the skew can indicate to the operator that a problem may exist. Also, the skew can also be nonsymmetrical, with one edge of the belt being ahead of the other. This can be a signal that a belt carrying roll is out of parallel alignment in relation to the other carrying rolls supporting the belt. This can lead to belt instability or problems in guiding the belt, resulting in belt damage if the belt runs into the machine frame, causing loss of the belt and expensive machine downtime required to install a new belt. Moreover, the problem is complicated by high machine speeds. As machine speeds approach 7000 fpm, it is virtually impossible to view the shape of the skew, making accurate assessment of the guideline with the naked eye difficult, if not impossible.
It is also desirable to have a method to determine and monitor the speed at which the belt travels. By measuring and monitoring belt speeds, the machine operator could accurately determine and set the draw, which is the difference between the speed of adjacent or sequential belts or between a belt and another rotating element. In the paper making process, the speed of a belt increases towards the dry end of the machine, where paper sheet transfers involve open draws between adjacent belts. Because of the speed differential between adjacent belts, the sheet is tensioned as it passes from section to section, with the amount of tension being related to the draw.
Presently, the operator of the machine relies upon computer assistance in setting the draw. The information is taken from the drive elements of the machines within each section of the papermaking machine. It is believed that the accuracy and reliability of the information used in setting the draw could be improved if it were instead taken from the belts, rather than the drive elements.
Slippage is the speed differential between the belt and a given rotating element that contributes to the movement of the belt. Slippage may be an indicator of problems associated with running the belt. It is known that slippage between the belts and the rotating elements could adversely affect the accuracy of information taken from the speed of the drive elements, so drive speed is not always a reliable measure of belt speed. Also, checking belt speed against the rotational speeds of the support rolls, press rolls and/or dryer cans provide an assessment of slippage. Too much slippage may be due to either improper belt tension or imminent failure of a rotating element's bearing. Also, the indication of the drive roll speed given by the computer could be inaccurate due to miscalibration or some other error. Slippage could lead to catastrophic belt failure in which for instance, the belt is torn off the machine. Slippage may shorten belt life due to abrasive wear on the belt. In any event, it is a problem that could result in economic loss due to machine downtime and belt replacement.
It is also desirable to monitor the width of the wet laid or dry laid product that is being manufactured. For instance, in a wet laid process such as papermaking, the formed paper sheet shrinks in the cross-machine direction as it progresses through the sections of a papermaking machine.
It is also desirable to have a means for detecting breaks in the wet laid or dry laid product that forms on the belt. One existing method calls for sensing intensity differences in reflected light between the wet laid product and the conveying belt. This method is problematic in that there are added costs of coloring the entire belt, limitations on belt colors, and belt disposal problems that arise because of coloring.
It is further desirable to have a system for guiding belts. A system of this kind could determine if belts shift or undulate in the cross machine direction while running. If a belt running at high speed shifts its position in the cross machine direction, it will become misaligned, and at high speeds, it may run off the normal path into the machine frame, causing loss of the belt, expensive downtime, as well as being a safety hazard to personnel. One existing method for guiding the belt and preventing this condition employs paddles located at the edges of the belt in order to send a signal to a movable guide roll to guide the belt. However, physical contact between the paddles and the belt will cause the belt to wear or ravel at the edge.
The prior art shows that there have been attempts at providing belts which, due to some object that is on or within the belt, can be used in systems that provide information to the machine operator. U.S. Pat. No. 5,403,447 discloses a system in a press section of a papermaking machine for monitoring and control of the running of the press felts. In this system, detector devices detect an alignment stripe on the felt or felts.
The detectors include oscillation detectors that permit detection of the oscillation of press rolls or related components. When optical detectors are used, it is possible to determine the direction and kind of identification stripes which makes it possible to find out the running direction or state of tension of each felt. No information is provided on what kinds of materials can be used to form the stripes.
U.S. Pat. No. 5,413,680 discloses a method of detecting microbiological fouling of felts used in paper making machines. A felt suspected of containing microbiological deposits is contacted with iodonitrotetrazolium and then examined for a predetermined color change confirming the presence of bacteria on the felt. The felt assumes a red color in the presence of at least one million colony forming units of bacteria per gram of dry felt within thirty minutes after the iodonitrotetrazolium has contacted the felt.
U.S. Pat. No. 5,614,063 discloses an inductive edge detector system for paper machinery. The edge detector system consists of a continuous belt with an edge dope with metallic particles therein, and an inductive sensor connected to the guide device and adjacent the edge dope. The inductive sensor sends a signal to the guide device indicative of the location of the continuous belt. The guide device moves the continuous belt transversely relative to the running direction of the belt within the machine, dependent on the inductive sensor signal.
The edge dope is formed along the edge and includes a plurality of metal or metallic particles disposed therein. A further aspect of the invention described in the '063 patent is the ability to determine the amount of "stretch" of the continuous belt under loading conditions.
International publication no. WO 97/27360 discloses an industrial roll cover comprising a polymer matrix, the polymer matrix comprising at least one thermochromic material. The thermochromic materials of the reference ideally provide a reversible color change, generally brought about by heat which causes the color forming compound to melt and come in contact with an electron accepting material. This can be used to provide information on the operating temperatures of the fabric.
Certain compositions are known to emit laser light in response to excitation by energy from an external laser source. U.S. Pat. No. 5,448,582 discloses an optical gain medium and is a multi-phase system wherein: a first phase is an electromagnetic radiation emitting and amplifying phase; a second phase is an electromagnetic radiation scattering phase; and a third phase is a transparent matrix phase. By example, the emission phase may consist of dye molecules, the scattering phase may consist of Al.sub.2 O.sub.3 or TiO.sub.2 particles, and the matrix phase may consist of a solvent such as methanol. A smallest dimension of a body comprised of the gain medium may be less than a scattering length associated with the scattering phase.
In one specific embodiment of U.S. Pat. No. 5,448,582 laser-like activity is generated in a laser excited methanol solution containing a dye, such as rhodamine, and high index contrast nanoparticles, such as TiO.sub.2 or Al.sub.2 O.sub.3. This system is also disclosed in U.S. Pat. No. 5,434,878. This gain medium exhibits many of the properties of an efficient laser source, and has a nearly thresholdless input-output behavior. A laser-like activity is intended to encompass a condition wherein a well defined excitation causes the output linewidth of the emission to be narrowed.
As set forth in U.S. Pat. No. 5,448,582 nearly threshold-less laser-like behavior is achieved in a strongly scattering optically pumped dye-methanol solution containing colloidal TiO.sub.2 or Al.sub.2 O.sub.3 nanoparticles. The emission from the optically pumped high gain colloidal medium is shown to exhibit a slope change in its linear input-output characteristics above a critical pump pulse energy. The change in slope is accompanied by a significant narrowing of the output spectral linewidth, with a bichromatic spectrum appearing at high pump energies with some dyes. Excitation of the colloidal medium with 80 picosecond pulses at 532 nm was found to result in an emission which was shorter than a 300 picosecond time resolution of an optical detection system, thus substantiating the occurrence of laser-like behavior and not mere fluorescent behavior.
A fiber monofilament or yarn exhibiting the properties of the aforementioned system is known in the art. These fibers or monofilaments are comprised of laser dyes and scattering particles contained within a polymer host. (Textile Rental, March 1997, p. 36-40). Suitable scattering particles and hosts are titania and nylon 6, respectively. Such fibers, when included in linens, provide a means of coding, tracking and preventing linen loss. The incorporation of the multi-phased system has also been incorporated into a coating or paint, making it possible to apply coatings having laser-like properties.